In prior surgical techniques wherein the patient's blood circulation system is diverted through an extracorporeal heart-lung circuit, it has been common to use a pair of venous return cannulas inserted in the neighborhood of the appendix of the right atrium of the heart. The auricular appendix is convenient for clamping purposes and is also conveniently located for cannulation. However, double cannulation is not easily accomplished through the appendix of the atrium, since there is insufficient space to insert the two cannula tubes.
The double incisions required for the above form of cannulation technique requires placement of two separate snare sutures for the cannulas surrounding the two individual incisions. This takes preparation time and increases the trauma to the area due to the two separate incisions. Furthermore, the two cannulas, once inserted, often obstruct the area and further delay the surgical process.
In the typical two cannula arrangement, a third cannula is used for infusion of blood from the heart-lung machine. This cannula is typically inserted into the aorta. The two drainage tubes and the infusion tube often hinder positioning of the heart to facilitate aortocoronary bypasses, valve implants, etc. In addition, the several tubes hinder direct access by the various surgical instruments used in such operations.
It becomes desirable, since the venous drainage cannulas lead to the same phlebotomy line of the extracorporeal circuit to use a single cannula inserted through a single incision in the atrial appendix.
U.S. Pat. No. 4,309,994 to Grunwald, co-inventor in this application, discloses a bifurcated cannula and internal obturator that are now in common use as a solution to the double cannulation problems indicated above. The cannula includes resilient branches at an inward end, one that is receivable within the superior vena cava and the other for descending the inferior vena cava. Both branches diverge from the central axis of a single tube. An obturator having a cross-sectional configuration matching the cross-sectional shape of the cannula is slidably received within the tube. The obturator includes relatively straight bifurcated legs that are used to hold the cannula branches together along the tube axis during initial insertion. The obturator legs also enable the cannula branch ends to separate within the atrium following initial insertion. the obturator is shaped along its full length to slidably engage the internal configuration of the cannula and branches to hold the cannula straight with the branches together to facilitate insertion of the cannula into the atrium and to prevent reflux of blood through the cannula by close frictional engagement of the obturator along the cannula. While this assembly has operated effectively, some difficulty has been experienced in insertion of the cannula and separation of the branches due to frictional resistance to axial movement of the obturator within the cannula.
U.S. Pat. No. 4,248,224 to Jones discloses a double venous cannula that makes use of a bifurcated cannula tube having an external obturator in the form of a second tubular member. The external obturator is received axially over the length of the primary cannula tube and includes an end that is used to cam the bifurcated cannula branches together and apart to facilitate insertion and removal of the cannula branches into the superior and inferior vena cavae. The cannula branches in this version extend from a crotch of the tube that remains exposed outwardly of the incision site. The incision is closed by purse sutures about the two separate branches of the cannula. The tissues engaged about the two individual branches may not be adequately gathered about the two tubes, especially in areas adjacent to the tangential points of contact of the two tubes. Interstices are therefore formed between the tubes and the adjacent tissues at the incision site. Unless these areas are otherwise plugged, the interstices will permit reflux of blood.
A double cannula arrangement is shown in U.S. Pat. No. 3,903,895 to R. D. Alley, et al. This patent shows a venous return line of an extracorporeal circuit with a double tubular end, one cannula end being inserted through an incision in the atrium and extending upwardly into the superior vena cava, while the remaining cannula is inserted through a second incision to descend into the inferior vena cava. The two branches extend outwardly of the heart to connect with converging lines to the heart-lung circuit.
U.S. Pat. No. 3,835,863 to Goldberg discloses a "T" tube that is used as a drainage catheter for implantation in an internal duct. Transverse arms of the "T" tube are slotted longitudinally to enable folding over one another to the diameter of the main tube branch. The tubes can thus be folded onto one another and inserted through an incision in the associated duct. Upon insertion, the two branches may spring apart, opening into the duct. Withdrawal of the tube is accomplished simply by pulling the tube outwardly. The transverse branches of the tube will fold together at the incision as the tube is pulled outwardly.
The Goldberg "T" tube may have beneficial use in the drainage of internal ducts such as bile ducts in abdominal surgery. However, such a drainage tube would not be functional for use as a venous return cannula due to the open slots formed along the two branches. Furthermore, the open tubes would not lend themselves easily to operation with an obturator by which the branch ends would be guided upon insertion or withdrawal through a single incision.
The preferred embodiments disclosed herein provide distinctive improvements that are not shown or suggested by the known prior art. The disclosed cannula and obturator include provisions that significantly ease insertion of the cannula and that facilitate placement of the cannula branches within the superior and inferior vena cavae with minimal manipulation.